This invention relates to measurement systems, and more particularly, to measurement systems having a capacitive sensor.
Capacitive sensors have often been used to provide the input signal for many forms of prior art transducer instrumentation, for example, scales or balances, accelerometers, and pressure transducers, or proximity gauges. In such systems, the precision at which measurements can be made is very much a function of the stability of the circuit interfacing the sensor portion and the read-out portion of the system. In general, the prior art systems have permitted relatively low precision measurements due to sensitivity of the interface circuit to combinations of various factors, such as drive signal wave shape and drive signal amplitude.
In practice, these shortcomings of the prior art systems have been in part overcome by systems, such as those disclosed in U.S. Pat. No. 4,093,915, where a feedback network is used for linearizing the nominal system output. While such systems are generally effective, in many applications, the feedback networks add substantially to the circuit complexity, and are correspondingly expensive.
Accordingly, it is an object of the present invention to provide a system for generating a signal linearly related to the capacitor reactance of a sensor capacitor.
Another object is to provide a system for determining the capacitance associated with a sensor capacitor with the system being substantially independent of the wave shape of the driving signal.